Evaluating Twenty Years of Microbial Contamination Tracer Usage in Ocean Drilling

Abstract:

When successful, deployment of microbiological contamination tracers is an essential component of sample quality control. However, anecdotes describing deployment or measurement failures range from silly to frustrating. We examined the data generated over the past twenty years of tracer usage on board the JOIDES Resolution to evaluate how well tracers perform and under what circumstances they are most reliable. Actual data is difficult to track; failed deployments are not always documented and analyses are not always completed. Despite these challenges, we identified 311 cores where fluorescent microspheres were deployed and fully analyzed as well as 403 cores where perfluorocarbon tracers (PFTs) were deployed and fully analyzed. A full analysis means that samples were taken from both core exterior (to confirm delivery) and interior (to confirm contamination or lack thereof). We find that PFTs have a higher rate of false positives than microspheres (27% relative to 4%) but that these issues may be ameliorated by using the less volatile compound perfluoromethyldecalin (PFMD). There is no correlation between penetration of microspheres and PFTs to sample interiors in the 91 core samples where both tracers were deployed. In conjunction with a new Technical Note updating recommendations on tracer usage, this study recommends that fluorescent microspheres no longer be used, and that PFMD be used instead of perfluoromethylcyclohexane (PFMCH). These recommendations derive not only from the data, but from the experiences of microbiologists at sea.